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<title>Host Config (GNU Compiler Collection (GCC) Internals)</title>

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<h2 class="chapter" id="Host-Configuration"><span>19 Host Configuration<a class="copiable-link" href="#Host-Configuration"> &para;</a></span></h2>
<a class="index-entry-id" id="index-host-configuration"></a>

<p>Most details about the machine and system on which the compiler is
actually running are detected by the <code class="command">configure</code> script.  Some
things are impossible for <code class="command">configure</code> to detect; these are
described in two ways, either by macros defined in a file named
<samp class="file">xm-<var class="var">machine</var>.h</samp> or by hook functions in the file specified
by the <var class="var">out_host_hook_obj</var> variable in <samp class="file">config.gcc</samp>.  (The
intention is that very few hosts will need a header file but nearly
every fully supported host will need to override some hooks.)
</p>
<p>If you need to define only a few macros, and they have simple
definitions, consider using the <code class="code">xm_defines</code> variable in your
<samp class="file">config.gcc</samp> entry instead of creating a host configuration
header.  See <a class="xref" href="System-Config.html">The <samp class="file">config.build</samp>; <samp class="file">config.host</samp>; and <samp class="file">config.gcc</samp> Files</a>.
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